Plans are to install a wood mantle over the current 73" brick one. As you can see, the bricks step down in depth size: 7.75 > 6.25 > 5.75 > 5 > 4.25 (total of 10.25 in height), then solid brick face another 39.5 down to the 15.5 deep hearth. Thoughts are to cover the top & add moulding only over the top (2.25") bricks, leaving the lower 4 runs.

So, what would be the best way to attach the new wooden mantle? Should I drill & use dowels + adhesive, or would adhesive alone suffice? The new mantle will probably be no more than 10" or so deep over the 7.75" depth now. Also, should I add lower moulding over more than just the top 2.25" tall run? Maybe at least over the top 2 runs for a total of 4.5" as the 73" length is so substantial?